It has been shown in Japanese Official Patent Publications (hereinafter referred to as Kokoku) No. S62-53033, No. S62-53034, Japanese Laid-Open Patent Application Publications (hereinafter referred to as Kokai) No. S58-103565, No. S58-103566, Kokoku No. S62-53035, and Kokai S58-104970 that coating of the surface of a silver-alloy powder with benzotriazole improves migration-resistant properties. However, when the silver powder surface-coated with benzotriazole or a commonly available silver powder is compounded with a curable organic resin composition, the powder impairs curability of the composition in storage.
Silver powders are used with curable silicone compositions as electrically conductive and thermally conductive fillers that improve electrical and thermal conductivity of the compositions. However, the surfaces of commonly available silver powders normally contain some residual lubricants used in the manufacturing process, such as higher fatty acids, metal soaps, higher aliphatic alcohols or their esters, higher aliphatic amines, higher aliphatic amides, polyethylene waxes, etc. The presence of these residuals on the surfaces of the fillers significantly impairs curability of the curable silicone compositions during storage and some time later may lead to complete loss of curability.
Kokai No. H7-109501, Kokai No. H7-150048, and Kokai No. H8-302196 contain some proposals aimed at a solution of problems associated with the use of a silver powder surface-treated with an organosilicon compound and of a curable silicone composition compounded with a silver powder. However, the aforementioned proposals still appeared to be insufficient for restricting the decrease of curability in storage of the aforementioned curable silicone compositions.
It is an object of this invention to provide: a silver-based powder that, when compounded with a curable organic resin composition, does not decrease curability of the composition in storage; a method for preparation of the silver-based powder with high efficiency; and a curable silicone composition that is characterized by reduced changes in curability over time during storage and by an ability to be cured into a cured product with electrical properties that have minimal changes over time.